Re: [PATCH v5 0/6] MR1628: ntdll: Implement Low Fragmentation Heap.

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about dlls/ntdll/heap.c:
> +/* affinity to tid mapping array, limits the number of thread-local caches,
> -
> - and additional threads will fight  for the global categories groups
> - */
>
> +static LONG next_thread_affinity;
> -
>
> +/* a category of heap blocks of a certain size */
> +struct category
> +{
> - /* counters for LFH activation */
> - volatile LONG blocks_alive;
> - volatile LONG blocks_total;
> - volatile BOOL enabled;
> -
> - /* list of groups with free blocks */
> - SLIST_HEADER groups;
> - struct group *affinity_group[32];

This array is intended to be accessed atomically by multiple threads, but a substantial number of elements reside in a cache line (assuming 64 byte cache line size).  This results in false sharing, which may impact performance compared to purely threaded heaps.